This invention relates to solid-state primary batteries comprising a lithium anode, an iodine cathode containing a charge transfer complex and a solid lithium iodide electrolyte doped with a 1-normal-alkyl-pyridinium iodide.
Many of electronic circuits presently used require a power supply which provides an output of high voltage but low current. Generally compact batteries reliably operable for a prolonged period of time are desirable for fulfilling such a requirement.
However, usual primary cells incorporating a liquid electrolyte have serious drawbacks. For example, the liquid electrolyte is liable to leak. This is a fatal drawback when the cell is used in a system in which the leakage of the electrolyte is not permissible if slightest. Another drawback is that they need a separator. The separator used in compact cells will cause internal short-circuiting when broken, while reducing the interior space for accommodating the active cell components.
Efforts have been made to overcome these drawbacks. For instance, research has been directed to the development of non-liquid type cells in which all the cell elements are in solid state. Among the cells of this type heretofore proposed, those with a lithium anode are featured by a high energy density.
The performance of solid-state cells depends largely on the ionic conductivity of the solid electrolyte used. Thus solid-state cells will have a high internal resistance and therefore deliver low output current when containing a solid electrolyte which has such a low conductivity that the electron conductivity of the cathode mixture of the cell is at least 100 to 1000 times as high as the conductivity of the electrolyte.
Liang et al., J. Electrochemical Soc., 123,453 (1976), have proposed a solid-state cell comprising a lithium anode, a cathode mixture of lead iodide and lead sulfide and a solid lithium iodide electrolyte doped with alumina. The solid lithium iodide electrolyte doped with alumina has a relatively high ionic conductivity of about 10.sup.-5 ohm.sup.-1.cm.sup.-1 at 25.degree. C., whereas the discharge reaction product of the cell is lithium iodide having a relatively low ionic conductivity of about 10.sup.-7 ohm.sup.-1.cm.sup.-1 at 25.degree. C.
Schneider et al., J. Power Sources 5,651 (1975), have proposed a solid-state cell comprising a lithium anode, a cathode mixture composed of a charge transfer complex of iodine with poly-2-vinylpyridine containing an excess of iodine, and a solid lithium iodide electrolyte. The electrolyte and discharge reaction product of the cell are both lithium iodide having a relatively low ionic conductivity of about 10.sup.-7 ohm.sup.-1.cm.sup.-1 at 25.degree. C. The cathode mixture which has a relatively low electron conductivity of about 10.sup.-4 ohm.sup.-1.cm.sup.-1 at 25.degree. C. is fully useful as such since the electrolyte used has a still lower conductivity of 10.sup.-7 ohm.sup.-1.cm.sup.-1. The cellnevertheless has the drawback of being unable to deliver a relatively high output current because of the low conductivity of the electrolyte and, moreover, remains to be improved in its shelf life. In fact, when the battery is stored at high temperatures, iodine diffuses markedly from the cathode mixture through the solid electrolyte, possibly draining the cell due to the attendant internal short-circuiting during storage.